The present invention relates to a releasable coupling for a power transmission line from a main transmission to the tail rotor of a helicopter.
Some helicopters comprise a tail section which is foldable substantially 180.degree. alongside the body to reduce the size of the helicopter, for example, when loading it onto a ship.
For the tail section to be folded, a releasable coupling must obviously be provided along the transmission line connecting the main transmission of the helicopter to the tail rotor.
Known couplings substantially comprise a pair of coupling assemblies fitted respectively to the body and tail section, and having respective transmission members connected angularly to the main transmission and tail rotor respectively. The two transmission members comprise respective saw-toothed face gears, which mesh when the tail section is in the work position to restore continuity of the power transmission line between the main transmission and the tail rotor.
Known couplings of the type briefly described above involve several drawbacks.
In particular, certain operating conditions (e.g. rough landing with no torque on the tail rotor, or torque inversion) may result in instantaneous release of the transmission members, so that torque is cut off along the power transmission line to the tail rotor.
Moreover, the face gears call for accurate alignment of the respective transmission members, which is difficult to achieve on account of the coupling assemblies being fitted to the structure of the helicopter, so that the dimensional accuracy achievable is fairly poor.